Reagents for Complexometric Titrations Complexometric Titrations
Sigma-Aldrich offers Fluka and Riedel-de Haën quality reagents for complexometric titration. The trademark IDRANAL® comprises aminopolycarboxylic acids (EDTA and analogs) and their volumetric solutions for use in metal determination by titration. On this page you’ll find more information on the correct choice of complexing agent, indicator, pH value, titration method and masking agents.
Complexometric titration:
Sigma-Aldrich offers Fluka and Riedel-de Haën quality reagents for complexometric titration. The trademark IDRANAL® comprises aminopolycarboxylic acids (EDTA and analogs) and their volumetric solutions for use in metal determination by titration. On this page you’ll find more information on the correct choice of complexing agent, indicator, pH value, titration method and masking agents.
Complexometric titration:
- Metal ions from the sample react with complexing agents (chelating agents) to create the complex
- Color change determines the end-point of the titration
Analytical applications:
- Determination of water hardness
- Determination of metal ions
Features & Benefits of Sigma-Aldrich’s complexometric reagents:
- Stability at high temperatures
- Readily soluble in water
- Form stable chelates with most metal ions over a wide range of pH and temperature
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| Factor and Titer of solutions |
When carrying out a titration using ready-to-use solutions or concentrates, it is important to pay attention to the given factor on the label of each package. This factor must be used to calculate the titer of the solution by multiplying it with the nominal concentration. For example, for a hydrochloric acid with nominal concentration of 0.1 mol/L and a factor of 1.001, the actual concentration is 0.1*1.001=0.1001 mol/L.
The titer t is the ratio of the actual concentration of a standard solution c(Χ)ACTUAL (actual value) and the desired concentration of the same solution c(Χ)NOMINAL (nominal value):
| t = | c(Χ)ACTUAL |
| c(Χ)NOMINAL |
As an example, for a standard solution of sulphuric acid of a nominal concentration c(H2SO4)NOMINAL = 0.1000 mol/L and an actual concentration c(H2SO4)ACTUAL = 0.1001 mol/L, the titer t is calculated as follows:
| t = | 0.1001 mol/L | = 1.001 |
| 0.1000 mol/L |
In order to obtain the consumption of a solution of concentration c(H2SO4) = 0.1000 mol/L, the volume of consumed sulphuric acid standard solution in the titration has to be multiplied by the titer t = 1.001.
The measured titer (factor) of the ready-to-use solutions is displayed on the certificate of analysis. However, for FIXANAL concentrates, the titer is adjusted to 1.000 (to a precision of ± 0.2 %) during the filling process.
With the titer so determined, the weight of the volume of liquid corresponding to exactly 0.1 mol of the specified analyte is calculated. This exact volume of liquid is added to every ampoule in the lot, using high-precision filling equipment. The variation of the resulting weight is < 0.1%; the typical standard deviation is lower than 0.04%.
The concentration of the liquid inside each FIXANAL ampoule may vary slightly from lot to lot but the amount of the specified material in each ampoule is exactly the same, for example 0.1 mol HCl (not mol/L !).
With the titer so determined, the weight of the volume of liquid corresponding to exactly 0.1 mol of the specified analyte is calculated. This exact volume of liquid is added to every ampoule in the lot, using high-precision filling equipment. The variation of the resulting weight is < 0.1%; the typical standard deviation is lower than 0.04%.
The concentration of the liquid inside each FIXANAL ampoule may vary slightly from lot to lot but the amount of the specified material in each ampoule is exactly the same, for example 0.1 mol HCl (not mol/L !).
| Ready-to-use solutions | FIXANAL® concentrates |
| Contain exact amount in terms of concentration (e.g. 1 mol/L) | Contain exact amount of substance (e.g. 1 mol) |
| Titer precision 1.000 ± 0.1 % | Titer precision 1.000 ± 0.2 % |
Every FIXANAL ampoule contains a precise given amount of a concentrate. This can be diluted to a final volume desired by the user. Usually, the concentrates are diluted to 1 L but other dilutions can also be prepared:
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The water used in dilution should be distilled and degassed; otherwise sluggish endpoints or changes of titer can occur.
The volume of a solution depends on temperature and therefore, temperature is an important marginal condition for all volumetric determinations.
The influence of temperature on aqueous solutions is ten times more than that on the glass, and averages ~0.02 % per degree Celsius. For example, when an aqueous standard solution prepared at 20°C is used at 25°C, its volume should be corrected using a factor of 0.999 if striving for an error considerably below 0.1%.
The following table shows the temperature-related dependences of:
- Density of water
- Volume of 1000 mL water (measured at 20°C); as an approximation also valid for aqueous standard solutions
- Correction factors for standard solutions prepared at 20°C (valid for Fluka ready-to-use standard solutions)
- Correction factors for standard solutions prepared at 25°C (e.g. standard solutions prepared at 25 °C by use of FIXANAL concentrates)
Note: No temperature correction is required when standard solutions made from FIXANAL concentrates are used at the temperature equivalent to that indicated for fill-up time.
Table ... Correction of temperature for volumetric solutions
| T / °C | Density Water (g/mL) | Volume (mL) of 1 L water at 20°C | Factor (solution prepared at 20°C) | Factor (solution prepared at 25°C) |
| 10 | 0.999699 | 998.50 | 1.0015 | 1.0027 |
| 11 | 0.999604 | 998.60 | 1.0014 | 1.0026 |
| 12 | 0.999497 | 998.71 | 1.0013 | 1.0025 |
| 13 | 0.999376 | 998.83 | 1.0012 | 1.0023 |
| 14 | 0.999243 | 998.96 | 1.0010 | 1.0022 |
| 15 | 0.999099 | 999.10 | 1.0009 | 1.0021 |
| 16 | 0.998942 | 999.26 | 1.0007 | 1.0019 |
| 17 | 0.998773 | 999.43 | 1.0006 | 1.0017 |
| 18 | 0.998595 | 999.61 | 1.0004 | 1.0016 |
| 19 | 0.998403 | 999.80 | 1.0002 | 1.0014 |
| 20 | 0.998203 | 1000.00 | 1.0000 | 1.0012 |
| 21 | 0.997991 | 1000.21 | 0.9998 | 1.0010 |
| 22 | 0.997769 | 1000.43 | 0.9996 | 1.0007 |
| 23 | 0.997537 | 1000.67 | 0.9993 | 1.0005 |
| 24 | 0.997295 | 1000.91 | 0.9991 | 1.0003 |
| 25 | 0.997043 | 1001.16 | 0.9988 | 1.0000 |
| 26 | 0.996782 | 1001.43 | 0.9986 | 0.9997 |
| 27 | 0.996531 | 1001.68 | 0.9983 | 0.9995 |
| 28 | 0.996231 | 1001.98 | 0.9980 | 0.9992 |
| 29 | 0.995943 | 1002.27 | 0.9977 | 0.9989 |
| 30 | 0.995645 | 1002.57 | 0.9974 | 0.9986 |
| 31 | 0.995339 | 1002.88 | 0.9971 | 0.9983 |
| 32 | 0.995024 | 1003.19 | 0.9968 | 0.9980 |
| 33 | 0.994701 | 1003.52 | 0.9965 | 0.9977 |
| 34 | 0.994370 | 1003.85 | 0.9962 | 0.9973 |
The ampoules are made of high-resistance polyethylene and have an attached funnel (see image aside). Simply twisting the ampoules opens the bottom outlet; a specially developed rinsing funnel facilitates the simple perforation of the diaphragm. The integrated deflector accelerates the complete rinsing of the concentrate. To make it easier for the user to mark the reagents, the ampoules are provided with self-adhesive labels, which can be easily attached to the storage vessel in the laboratory.
If made necessary by the chemical properties, the products are contained in black pigmented PE ampoules or in glass ampoules without the twist-opening mechanism. Naturally, all ready-to-use solutions and FIXANAL concentrates are calibrated against independently produced reference standards. All chemicals and test equipment are examined according to the rules of DIN EN ISO 9001 and DIN EN ISO 14001.
If made necessary by the chemical properties, the products are contained in black pigmented PE ampoules or in glass ampoules without the twist-opening mechanism. Naturally, all ready-to-use solutions and FIXANAL concentrates are calibrated against independently produced reference standards. All chemicals and test equipment are examined according to the rules of DIN EN ISO 9001 and DIN EN ISO 14001.
Quality Assurance, Packaging and Handling
- FIXANAL ampoules are subject to strict production and quality control specifications
- A special ampoule-sealing process guarantees titer to be accurate within specified shelf life
- Ampoules are supplied with self-adhesive labels that can be easily attached to the storage vessel
- Ampoules are made of high-resistance polyethylene (PE), natural or black-pigmented, or glass, depending on the content
- PE-ampoules have an integrated rinsing funnel for perforating the membrane (see Figure 1); the integrated deflector accelerates complete rinsing of the concentrate from the ampoule
- Glass ampoules do not have the twist-opening mechanism; instead a glass rod is used for piercing both ends of the ampoule (see Figure 2)
- The water used to fill up to volume should be distilled and degassed, otherwise sluggish endpoints or changes of titer can be observed
- Concentrates of iodine, containing iodide-iodate-mixtures, have to be treated with an equivalent amount of acid (+ 1% excess) before bringing them up to volume, in order to react to free iodine
- Traceability and reference materialsAssuring the traceability of reagents is an elaborate and often difficult process. In order to help analytical customers with this laborious task, Sigma-Aldrich offers accurate and traceable volumetric solutions tested against EMPA, BAM and/or NIST standard reference materials. Certified reference materials are reliable, readily quantifiable substances of high purity, low reactivity and hygroscopicity, high solubility and high equivalent weight.
Major international organizations for reference materials, accreditation and certification:- BAM German Federal Institute for Materials Research and Testing
- EMPA Swiss Federal Laboratories for Materials Testing and Research
- NIST National Institute of Standards and Technology, USA
NIST is responsible for developing, maintaining and disseminating national standards and also the realizations of the SI for the basic measurement quantities and derived measurement quantities. NIST is also responsible for assessing the measurement uncertainties associated with the values assigned to these measurement standards. EMPA and BAM are similar institutions to NIST, and are officially accredited to certify standards.
The resulting certification is the one stated by ISO Guidelines 30–35. The EMPA/BAM certified reference standards have two important advantages:- Strict separation between manufacturers and institutes for certifications
- Two independent methods are used from two independent institutes
Examples of certified reference materials used at Sigma-Aldrich (certified by BAM/EMPA, traceable to NIST) for analyzing the volumetric solutions:
Sodium carbonate
Hydrochloric acid
Sodium chloride
Silver nitrate
Potassium hydrogenphthalate
Perchloric acid
Potassium permanganate
Potassium iodate
Sodium thiosulfate
Several aspects of the Certified Volumetric Solutions combine to help ensure their high quality:- Throughout their production and quality control, volumetric solutions are handled with extreme care. The reliability of the test equipment and the quality of the products are continuously monitored by means of a system of in-process controls and final checks.
- For analysis, different titration instruments are used to adjust the titer against a certified EMPA/BAM reference material, which is regularly compared with a NIST standard reference material during the certification process. This guarantees that the reference material is tested and certified with the know-how of several different institutions with established worldwide reputations.
- The material that was actually used for the determination of the titer is listed on the certificate of analysis for each lot.
- BAM German Federal Institute for Materials Research and Testing
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